(1) Field of the Invention
This invention pertains to a system for recovering and diagnosing faults in a PCM digital switching system and more particularly to a system for the insertion of test PCM samples into the PCM data stream of a digital switching network and subsequent examination for fault of these test PCM samples.
(2) Description of the Prior Art
In electronic digital switching systems, duplex PCM networks with comparison between each of the network copies is known in the art. One such switching system is the GTD-4600 which is designed and manufactured by GTE Automatic Electric Incorporated. The maintenance aspects are further discussed in an article entitled "GTD-4600 Peripheral Equipment Maintenance" in the GTE Automatic Electric Journal, March, 1978. The GTD-4600 provides both comparison and parity checking for the PCM samples in the network.
In the GTD-4600 when a miscomparison is detected without a parity error, the recovery software would propogate PCM samples with the bad parity through the network and determine which network copy was operating correctly. As a result, the GTD-4600 network recovery system could only detect failures effecting single bits or all bits of the PCM samples.
In contrast, the present invention provides the ability to insert test PCM samples into the network and to trap the resultant output. As a result, this invention permits the insertion of any twelve bit pattern into the network and provides for a bit by bit analysis of each network output.